Synchronous / asynchronous, blocking / non blocking and IO

Synchronous and asynchronous

• The key ： Can you Work at the same time
  

Blocking and non blocking

• The key : Can you dynamic

A combination of two

Synchronous blocking

• Possible performance ： A thread is waiting
  

Synchronous nonblocking

• Possible performance ： A thread is running normally
  

Asynchronous blocking

• Possible performance ： Multiple threads are waiting

Asynchronous non-blocking

• Possible performance ： Multiple threads are running normally
  

I/O operation

• The process 1： Wait for the data
• The process 2： Reading and writing 、 Copy the data

Blocking IO And non blocking IO

• Blocking IO： User processes participate in the above two processes , Blocked in IO Process
  

• Non blocking IO： User processes do not need to participate in the above two processes , When it's done , The kernel notifies the user thread
  

asynchronous IO And signal driven IO

• Signal driven IO： When descriptor data is ready , By producing SIGIO The signal initiates a call to the application signal correlation function , Applications can be accessed through recvfrom Copy data （ You also need to copy it yourself ）
  
• asynchronous IO： The application program can return immediately after triggering the system call , The kernel sends a signal to the application after the data copy is completed , Trigger application logic .（ You don't need to copy it yourself ）
  

Model comparison